Just to make sure everyone is on the same page, what most people know as milkshakes are called cabinets in RI (origin unclear), and frappes (pronounced frap, not frappay) north of Boston. The Creamery is a good place to start.

To really find a good shake must be difficult but its just very chilled milk, a bit of ice cream and flavored syrup. Coffee syrup came in via Ma. and a blender type of machine was kept in a Cabinet thus the infamous coffee cabinet.